粗煤气管道中，应该保证下降管倾角（）
A.>40°
B.<40°
C.=40°
D.不确定
参考答案：A
正方体棱长扩大2倍，体积扩大______倍．
I need your help because I don’t know __________.
A．how to do
B．what to do it
C．what should I do
D．how to do it
